Histamine, which is a biogenic amine, plays a central role in the immune and inflammatory response and is also a neurotransmitter. For example, histamine controls various functions of antigen-presenting cells (dendritic cells and macrophages), T cells, B cells, epithelial and endothelial cells, and proliferation of T cells or cytokine secretion in dendritic cells and mast cells (JDDG, 2010, 8, 495-504). There are 4 histamine receptors (histamine 1 receptor, histamine 2 receptor, histamine 3 receptor and histamine 4 receptor) (Br. J. Pharm 2006, 147, S127-S135). An acute allergic reaction is controlled by the histamine 1 receptor which is distributed ubiquitously in the body (Br. J. Pharmac. Chemother. 1966, 27, 427-439) and a gastric acid secretion is controlled by the histamine 2 receptor which also are distributed ubiquitously in the body like histamine 1 receptor (Nature 1972, 236, 385-390). It is well known that the neurotransmitter secretion in the central nervous system is controlled by the histamine 3 receptor which is expressed in neurons (Nature 1983, 302, 832-837). The histamine 4 receptor further explains physiological functions of many signaling processes which are not explained only by the histamine 1 receptor, histamine 2 receptor and histamine 3 receptor. The histamine 4 receptor was reported for the first time in 1994 and its cloning was performed only since 2000. The histamine 4 receptor, which is a G-protein coupled receptor, consists of 390 amino acids and is activated by binding with Gi/o protein to increase calcium concentration or suppress cyclic adenosine monophosphate (cAMP) (The Open Immunology Journal, 2009, 2, 9-41). The histamine 4 receptor is mainly expressed in bone marrow or eosinophils, basophils, T cells, mast cells, monocytes and dendritic cells, and is also observed in the spleen, thymus, lung, heart and intestines (Nat. Rev. Drug Discov. 2008, 7, 41-53; Biochem. Biophys. Res. Commun. 2000, 279, 615-620). The histamine 4 receptor not only plays a central role in the immune response but also has effects on the activation and migration of various immunocytes, and the production of cytokines and chemokines (J. Immunol. 2005, 174, 5224-5232; J. Pharmacol. Exp. Ther. 2003, 305, 1212-1221; J. Allergy Clin. Immunol. 2007, 120, 300-307; J. Recept. Signal Transduct. Res. 2002, 22, 431-448).
In various in vivo experiments, it is well known that the histamine 4 receptor plays an important role in inflammation and itch (J. Allergy Clin. Immunol. 2007, 119, 176-183; J. Pharmacol. Exp. Ther. 2004, 309, 404-413). Especially, as results of researches, it has been found in an allergic mouse asthma model that the histamine 4 antagonists alleviate lung inflammation by controlling Th2 (T helper type 2) reaction, and confirmed that histamine 4 antagonists effectively suppress histamine-induced itch. Such a dual effect against allergic inflammation and itch is a basis for the fact that the histamine 4 receptor may be a good target for treating allergic skin diseases such as atopic dermatitis (J. Invest. Dermatol. 2010, 130(4), 1023-1033).
In such an immunocyte, antagonism against the various functions of the histamine 4 receptor is a key focus of study of inflammatory diseases, pruritus, pain, allergic rhinitis, asthma, rheumatoid arthritis, atopic dermatitis, idiopathic chronic urticaria, inflammatory pain, neuropathic pain and osteoarthritic pain. In addition, a recent study related to effectiveness of the histamine 4 receptor against cancer has been announced, and thereby its development as an anti-cancer drug is expected.
Recently, it has been reported in WO2010/030785 that quinoxaline-based derivatives show activity on the histamine 4 receptor. However, they did not show a sufficient pharmacological in vivo activity in animal model because their solubility and metabolic stability are not high.